Diffusion transfer processes which employ the formation of a soluble silver complex and the reduction of this complex in the presence of physical development nuclei are well known, as is the application of these processes to obtain either a positive, metallic silver photographic image or, in the case where the physical development is also associated with a dye forming substance, a positive color photographic image. See British Pat. No. 904,364, page 19, lines 1-41.
In many such processes, it is desirable to obtain physical development yielding a silver image the density of which is as high as possible. For this purpose, various intensifying means have been proposed in the prior art; in particular, organic substances have been used such as heterocyclic mercaptans which make it possible, due to their ability to react with the developed silver, to intensify the black appearance of silver images.